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Weaning: the spontaneous breathing trial and the RSBI

The question is not whether the patient is comfortable on the ventilator. It is whether they still need it today.

William Owens, MD, Attending Intensivist Physician · Updated 2026-10-05

Ask every day

Time on a ventilator carries its own harms: pneumonia, delirium, weakness that outlasts the admission. The default should be a daily assessment of whether the tube can come out, not a wait for the patient to look obviously ready.

Readiness

• FiO2 at or below 0.5.
• PEEP at or below 8 cmH2O.
• Hemodynamically stable, with no escalating vasopressor requirement.
• Awake enough to follow commands.
• Not needing frequent suctioning.
• Not on an unconventional mode.

These are gates, not a score. The underlying reason for intubation also has to have improved; a patient can meet every line above and still have the airway problem that put them there.

Running the trial

CPAP of 5, or pressure support of about 7, for 30 to 60 minutes. Longer adds fatigue rather than information.

Stay and watch the first few minutes. Most failures declare themselves early, and the ones that do not are usually about endurance rather than capacity.

The rapid shallow breathing index

A patient breathing 24 times a minute at 350 mL has an index of about 69. The same patient at 32 times a minute and 250 mL is at 128, and the number has told you what the pattern already showed: fast and shallow is the signature of a patient working too hard to keep it up.

It is a supporting measurement, not a verdict. Extubating on a good index while the patient looks terrible is how an index gets a bad reputation.

Stop the trial for any of these

• Oxygen saturation below 88 percent.
• A heart rate rise of more than 20 beats per minute.
• A significant change in blood pressure in either direction.
• Sweating.
• Accessory muscle use.
• Paradoxical abdominal movement.

A failed trial is information, not a setback. Put the patient back on support that genuinely rests them, find the reason, and try again tomorrow.

Passing a trial is not the same as being extubatable

The trial tests the lungs and the respiratory pump. It does not test whether the patient can protect an airway, clear secretions, or manage without the tube that is currently holding a swollen upper airway open. Those are separate assessments and they fail separately.